Just because you had the original affair doesn't mean that you have to allow her to have one does it?
Drop all pursuit and pressure. Let her think that you too have given up. Nothing wrong with you saying you won't share her with another man.
It should be kind of like a shoulder shrug attitude with her...
Oh well, I did try and I did apologize and I did try to make things right, but I can't and I WON'T force her to love me or stay with me anymore than she could force me... Maybe it is over between us... Then kind of like turning around and walking the other way and not looking back...
That would be my approach....... Who knows. Maybe once she really has this guy without you in the backround he won't be looking like Cary Grant and Clint Eastwood all rolled into one person...
Then I would do what I want when I want and how I want with whomever I want...